Silicate-based compositions for binding particulate matter are well-known in the art. For example, U.S. Pat. No. 3,137,046 teaches the use of a binary mixture of an aqueous alkali metal silicate solution and a cyclic alkylene carbonate such as propylene carbonate to prepare foundry molds suitable for casting applications.
Many variations and refinements of alkylene carbonate/ silicate binder compositions have been developed in attempts to improve the curing characteristics or mechanical properties of such systems.
U.S. Pat No. 4,213,785 and Czech No. 234,936 teach the use of an alkyl or glycol ester of a carboxylic acid in combination with the alkylene carbonate and silicate to shorten the set time of the binder composition.
Brit. Pat. No. 2,045,777 teaches that the ability to recycle sand recovered from foundry molds is improved by the use of a high purity sugar with an alkylene carbonate hardener. The set time is not significantly affected by the sugar.
U.S. Pat. No. 4,233,076 teaches that extraction of the sand located within the cavities of a metal casting prepared using an alkylene carbonate/silicate binder is facilitated by the addition of a finely divided alumina, which acts as a demolding agent.
Jpn. Pat. No. 63-105092 teaches the use of mixtures of alkylene carbonates and carboxylic acids such as acetic acid in binder compositions. The set time is shortened by increasing the amount of carboxylic acid employed.
Due to productivity demands and the seasonal temperature changes which may occur in a foundry, excavation site, or other industrial setting, the ability to control set time is highly important. In particular, it is desirable to use a binder composition in which the reactivity can be readily adjusted as needed by variation of the relative proportions of the composition components. At the same time, the mechanical integrity of the foundry mold should not be compromised by these changes in binder composition. The components of the binder should be low in toxicity and odor so that the composition may be safely handled using ordinary precautions.